1. Field of the Invention
This invention relates to a mobile crane comprising a telescopic boom, which is pivoted to the rotating superstructure or rotating deck of the crane and is adapted to be luffed by a luffing cylinder, which is pivoted to the boom and the rotating deck. Also provided are a guying yoke, which is pivoted on the rear of the telescopic boom near the middle of its base box, two axially aligned, spaced apart rope pulleys, which are rotatably mounted at the outer end of the guying yoke, a reversing rope pulley, which is provided adjacent to the top end of the telescopic boom, and a winch provided with a rope, which serves to guy the telescopic boom and extends around one rope pulley of the guying yoke to the upper reversing rope pulley and back around the other rope pulley of the guying yoke to a fixed point.
2. Description of the Prior Art
Published German application 31 13 763 discloses a mobile crane which is of the kind described hereinbefore and in which the winch and the point to which the rope is fixed are disposed on mutually opposite sides of the telescopic boom approximately on the pivotal axis on which the guying yoke is pivoted to the telescopic boom. The guying yoke is guyed to the telescopic boom by ropes of constant length, which extend from the outer ends of the guying yoke to the bottom point of the base box of the telescopic boom. To permit the use of the additional ropes for exerting tension on the guying yoke, the additional ropes may be secured to the piston rod of a tension cylinder, which is pivoted to the base of the base box.
The guying telescopic boom of the mobile crane known from Published German application 31 13 763 involves time-consuming operations because the boom is guyed not only by the rope that is tensioned by the winch but also by ropes of constant length, which are permanently installed and may additionally be tensioned by a hydraulic cylinder. In the known mobile crane, the winch assembly must be controlled depending on the length of the boom and/or on the load and/or the inclination of the boom, and additional work is required for that purpose.